The present invention relates to stable growing media, such as plugs, for the germination of seeds and the growing or propagation of plants, and a method of manufacturing such growing media.
Plant seedlings or shoots can be planted in and grown in rooting media comprising soil mixture and a synthetic binder therefor, such as an organic resin polymer. Such rooting media or grow plugs eliminates the need to use pots, which add substantial weight and cost to transportation of plants. Such grow plugs are known, as is evident from U.S. Pat. No. 3,805,531, which discloses a rooting media formed by mixing a prepolymer with aggregate or soil mixture and adding water to the mixture. Upon curing of the prepolymer, a cohesive mass is formed. Similarly, U.S. Pat. No. 4,175,355 discloses soil plugs using a mixture of soil material comprising at least 15% polyurethane by weight on a dry basis of the soil material. A slurry is prepared by intensively mixing the prepolymer, soil material and water. The slurry is then cast into a die and after at least partial hardening of the polyurethane resin forming material, the resulting plug is removed from the die.
Because of the relatively high percentage of polyurethane in the plugs of the prior art, growing of the seedling is impeded. Indeed, it is generally believed that the less synthetic material in such plugs, the better the seedlings grow. Presumably the presence of the synthetic material impairs access of water and air to the plant roots. Ideally, therefore, grow plugs would contain no synthetic material. However, the synthetic material is a critical component of such plugs in order to provide a self-supporting, stable plug that does not disintegrate upon handling. Indeed, U.S. Pat. No. 4,175,355 discussed above expressly teaches that using less than about 15% polyurethane resin by weight on a dry basis results in the rooting media crumbling and falling apart. Moreover, plugs having a high concentration of polyurethane tend to be rubbery and insufficiently dense. As a result, the water retaining properties of such plugs are poor, and the penetration of air is impaired.
It would thus be highly desirable to produce a grow plug that mimics, as closely as possible, growing media that is free of synthetic material.
U.S. Pat. No. 5,209,014 discloses moulds for growing seedlings, the moulds being formed of turf, water, nutrients and a synthetic molding materials such as a polyurethane resin. The '014 patent states that the prepolymer is added in the amount of about 6 to 8% by weight to the turf mixture, the turf mixture first having been ground in a turf grinder. It is apparent from the disclosure that in referring to 6-8% prepolymer by weight of the dry mass, the term "dry mass" is being used to indicate turf mixture to which additional water has not yet been added.
That is, the turf mixture inherently contains moisture, and the "dry mass" referred to in the '014 patent includes that moisture, but does not include the water introduced to the turf mixture prior to the addition of the prepolymer. Were the amount of prepolymer in the '014 patent calculated on a true "bone dry" basis to be consistent with the other prior art, the percentage of prepolymer would be considerably more than the 6-8% disclosed.
It is therefore an object of the present invention to provide cohesive, stable, resilient, homogeneous, integral, self-supporting growing media with minimal amounts of synthetic material.
It is a further object of the present invention to provide growing media having improved water retaining properties and increased air space.
It is a still further object of the present invention to provide a process for preparing cohesive, stable, resilient, homogeneous, integral, self-supporting growing media with minimal amounts of synthetic binding material.